5G networks will allow for various degrees of Radio Access Network (RAN) centralization, varying from no centralization D-RAN (Distributed), to fully Centralized-RAN (C-RAN). In order to allow for such varying degrees of RAN centralization, 5G mobile transport networks will be required to support RAN functional splits in a flexible manner. Thereby, the division between fronthaul, which is the interface between a radio unit (RU) and an associated centralized-processing unit (CU), and backhaul, which is the interface connecting base stations and the mobile core, will blur since varying portions of functionality of the base stations will be distributed across the transport network. In this context, a new generation of transport network is proposed for 5G, namely crosshaul, integrating multi-technology fronthaul and backhaul segments into a common transport infrastructure.
Centralizing base station (BS) functionality as much as a possible at a CU can have significant advantages in reducing operational costs by providing, e.g., common refrigeration, single-point maintenance, etc. Furthermore, centralization of base station functionality can achieve higher capacity gains by providing, e.g., joint signal processing, coordinated resource allocation, etc. However, transport requirements for the fronthaul, e.g. network capacity, delay, jitter, etc., are very tight and can become more stringent when more functions are centralized at a CU. For example, Table 1 below provides analysis of a functional split described in Small Cell Virtualization Functional Splits and Use Cases from Small Cell Forum, Release 6.0 Version 159.06.02 issued on Jan. 13, 2016.
TABLE 1Table 1: Functional splits analysis: 1 user/TTI, 20 MHz BW, IP MTU 1500B; DL: MCS,2 × 2 MIMO, 100RBs, 2 TBs of 75376 bits/subframe, CFI = 1; MCS 23, 1 × 2 SIMO,96 RBs, 1 TB of 48936 bits/subframeDL/UL BWDelayBS FunctionalRequirementRequirementSplit #Decomposition(Mb/s)(μs)GainsARRC-PDCP151/4830,000Enables L3 functionality for multiplesmall cells to use the same HWEnhanced mobility across nodes w/ointer-small cell dataforwarding/signallingReduced mobility-related signalling tothe mobile core segmentNo X2 endpoints between small cellsand macro eNBsControl plane and user plane separationBPDCP-RLC151/4830,000Enables L3 and some L2 functionalityto use the same HWCRLC-MAC151/486000Resource sharing benefits for bothstorage and processor utilizationDSplit MAC151/496000Synchronized coordination and controlof multiple cellsCoordination across cells enables CA,CoMP, eICIC or cross carrierschedulingEMAC-PHY152/49250Enhancements to CoMP with RU framealignment and centralized HARQFPHY Split I 173/452250More opportunities to disable parts ofthe CU at quiet times to save powerGPHY Split II 933/903250Central L1 CU can be scaled based onaverage utilization across all cellsHPHY Split III1075/922250Smaller CU results in less processingresource and power savingIPHY Split IIIb 1966/1966250Enhancements to joint reception CoMPwith uplink PHY level combiningJPHY Split IV 2457.6/2457.6250
A centralized software defined network (SDN) control approach for integrated fronthaul and backhaul network resource management is described in PCT/EP 2016/057357. In the centralized SDN control approach described therein, data plane nodes inform the centralized SDN controller upon detecting any link or node changes via a control channel. Then the SDN controller decides whether it is necessary to update configuration settings for data plane network resources (e.g. data plane nodes) in order to react to the corresponding changes, and if deciding that such an update is necessary, triggers the update of the data plane network resources via the control channel. In response, the data plane network resources (e.g. data plane nodes such as the RU, CU, base stations, forwarding nodes such as switches and routers, etc.) will apply necessary changes to effectuate the update.